1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) device, and more particularly, to a driving method for local dimming of an LCD device to prevent color mixing in each block and reduce power consumption, when color backlights are driven by local dimming, and an apparatus using the same.
2. Discussion of the Related Art
Recently, flat panel displays have been popular as video displays, such as LCDs, Plasma Display Panels (PDPs), Organic Light Emitting Diodes (OLEDs), etc.
An LCD device includes a liquid crystal panel for displaying an image on a pixel matrix relying on the electrical and optical characteristics of liquid crystals that exhibit anisotropy in dielectric constant and refractive index, a driving circuit for driving the liquid crystal panel, and a backlight unit for irradiating light onto the liquid crystal panel. The gray scale of each pixel is adjusted by controlling the transmittance of light that passes from the backlight unit through the liquid crystal panel and polarizers through changing the orientation of liquid crystals according to a data signal.
In the LCD device, the luminance of each pixel is determined by the product between the luminance of the backlight unit and the light transmittance of liquid crystals that depends on data. The LCD device employs backlight dimming method for the purposes of increasing a contrast ratio and reducing power consumption. Backlight dimming is a technique that controls backlight luminance and compensates data by analyzing an input image and adjusting a dimming value based on the analysis. For example, a backlight dimming method intended for reducing power consumption reduces the backlight luminance by decreasing the dimming value and increases the luminance through data compensation. Thus the power consumption of the backlight unit is reduced.
Light Emitting Diode (LED) backlight unit using LEDs as a light source have recently been used for a backlight unit. The LEDs boast of high luminance and low power consumption, compared to conventional lamps. Because the LED backlight unit allows for location-based control, they may be driven by local dimming. According to the local dimming technology, the LED backlight unit is divided into a plurality of light emitting blocks and luminance is controlled on a bock-by-block basis. Local dimming may further increase the contrast ratio and decrease the power consumption since the backlight unit and the liquid crystal panel are divided into a plurality of blocks, local dimming values are decided by analyzing data on a block basis, and data is compensated based on the local dimming values.
Although white (W) LEDs that emit white light are typically used as the LED backlight unit, color backlight unit using at least 2-primary color LEDs, that is, color LED backlights with Red (R)/Green (G)/Blue (B) LEDs may be adopted to increase color reproducibility. An LCD device with color LED backlight unit uses a driving method for color local dimming, in which R/G/B LEDs are individually controlled in each block by individually analyzing R/G/B image data on a block basis.
However, since color local dimming is applied to a limited number of blocks, color mixing may occur in a block in which an achromatic color coexists with a pure color with a high chroma, thus degrading the color purity of an input image.